PC users personal configurations disappear!

I am using XP Pro SP 2 and have suddenly started getting a very strange problem. My computer has an Administrator (which is me), myself (as a limited account for daily use) and two other users each with their own log in password and configurations.

Suddenly last Saturday things went haywire and if either of the other two users actually logs off, rather than just change user, their configuration in totally lost when they log on again. I have not tested my own log on as I have already re-set up the other 2 users 3 times and don't want to risk losing my own configuration.

The only thing I did immediately prior to this problem was to run my regular weekly anti-spyware checks with AdAware and SpyBot so can't see any reason for this.